This application is based on applications No. 11-49895 filed in Japan on Feb. 26, 1999 and No. 11-154714 filed in Japan on Jun. 2, 1999, the content of which incorporated hereinto by reference.
This Invention relates to a fuse melted and cut off by heat when overcurrent flows and a battery pack containing the fuse.
A fuse is melted and cut off by heat when overcurrent flows, and thereby it interrupts current. A fuse is heated by Joule heat. Joule heat increases in proportion to the product of the square of current and resistance of the fuse. Therefore, when current becomes large, Joule heat abruptly increases and a fuse is heated to a high temperature. A fuse is melted at a predetermined temperature which is decided by the kind of the metal used for the fuse. Therefore a fuse is melted and cut off by heat when predetermined current flows and thereby current is interrupted.
It is important that a fuse melted and cut off by predetermined current can be rapidly melted and cut off and can surely interrupt current when current becomes a predetermined value. Further, it is also important that a fuse, after melted and cut off, can be kept in separated state and can continuously interrupt current. Fuses have been developed in which a spring member is used so as to surely interrupt current after a fuse is melted and cut off. Such fuses are disclosed, for example, in Japanese Patent Publication No. 114101 of 1995 and Japanese Non-examined Patent Publication NO. 29481 of 1995. In fuses disclosed in the abovementioned Publications, a spring member is connected in an elastically deformed state by means of a conductive substance of low melting point such as a solder. For example, as shown in FIG. 1, one end of a spring member 6 constituting a fuse is connected to a terminal 8 by means of a solder 7, in this Figure, when a conductive substance of low melting point such as a solder is melted by overcurrent, and the conductive substance becomes unable to connect the fuse comprising the spring member 6 in the elastically deformed state, so that as shown in FIG. 2, one end of the spring member 6 is separated from the terminal 8.
As shown in FIG. 1, a fuse comprising a spring member is not re-connected in current interrupting state. Therefore, such a fuse has an advantage that it can keep current interrupting state. However, since a fuse having this structure is melted and cut off at a portion connected to a terminal, the terminal and the spring member need to be fixed to a predetermined position. And whole of such a fuse becomes large in size, and it has a difficulty in being conveniently fitted to a narrow position. Further, in a fuse having this structure, since a conductive substance of low melting point such as a solder is melted to interrupt current, it is difficult to precisely set the value of current to be interrupted. It is very important for a fuse to precisely set the value of current to be interrupted. In a fuse having this structure, temperature and current at which a solder is melted change according to welding condition of the solder to a terminal such as amount of the solder. This makes it difficult to precisely set the value of current to be interrupted, which is hereinafter referred to as xe2x80x9cinterruption currentxe2x80x9d. Further, it is difficult to widely change melting temperature of a solder, in other words, widely change interruption current. It is especially difficult to make interruption current small. It is because, by reducing the amount of solder used for connecting a spring member to a terminal so as to make interruption current small, the spring member cannot be surely connected to the terminal.
The present invention has been developed in order to solve the abovementioned problems of the prior art. An important object of the present invention is to provide a fuse capable of precisely setting interruption current, of widely changing interruption current and further of being rapidly melted and cut off by interruption current and thereby interrupting current, and to provide a battery pack containing such a fuse.
Another important object of the present invention is to provide a fuse of a compact size which is conveniently applicable to a variety of uses.
The above and further objects of the present invention will more fully be apparent from the following detailed description given with accompanying drawings.
A fuse according to the present invention is a fuse melted and cut off by overcurrent, and it comprises a different thermal expansion coefficient metal laminate in which a plurality of metal plates of different thermal expansion coefficients are laminated. When a fuse is heated by overcurrent and thereby melted and cut off, a mechanical deforming force is applied to a melting portion of the fuse, which force being caused by difference between the thermal expansion coefficients of the laminated metals. In this specification, the word xe2x80x9cdifferent thermal expansion coefficient metal laminatexe2x80x9d means a laminate in which a plurality of different thermal expansion coefficient metal plates are laminated, and is used in wide meaning as including a bimetal in which two kinds of metal plates are laminated, a trimetal in which three kinds of metal plates are laminated, and a laminate in which more than four kinds of metal plates are laminated.
A fuse having this structure is advantageous in that it can precisely set interruption current, can widely change interruption current and further, can be rapidly melted and cut off by interruption current to interrupt current. It is because, when such fuse is heated by overcurrent and thereby melted and cut off, a mechanical deforming force is applied to melted portion, which force is caused by difference between the thermal expansion coefficients of the metal plates constituting a different thermal expansion coefficient metal laminate. When a different thermal expansion coefficient metal laminate is heated by overcurrent, different amount of deformation is generated through the laminate, which causes a mechanical deforming force to be applied to a melting portion of the fuse. With this mechanical deforming force, a fuse is precisely and rapidly melted and cut off at the melting portion. Therefore, a fuse having this structure can realize advantages of precisely setting interruption current, of widely changing interruption current, and further, of rapidly being melted and cut off by interruption current to interrupt current. Further, a fuse having this structure has an advantage of surely cutting off melted portion to interrupt current, since the melting portion of the fuse is thermally mechanically deformed and cut off by means of a different thermal expansion coefficient metal laminate.
Furthermore, unlike a conventional fuse, a fuse having this structure is not melted and cut off at a portion connected to a terminal, but is cut off at the melting portion to which a mechanical deforming force is applied by difference between thermal expansion coefficients of the metal plates constituting the different thermal expansion coefficient metal laminate, so that the whole of a fuse need not be large in size, and it can be conveniently fitted to a narrow portion. In other words, the whole of a fuse having this structure can be formed compact in size and conveniently applied to a variety of uses.
A fuse according to the present invention may comprise, for example, NIxe2x80x94Fe as a low thermal expansion coefficient metal and Cuxe2x80x94Nixe2x80x94Mn as a high thermal expansion coefficient metal.
Further, a fuse according to the present invention can be rapidly melted and cut off when current becomes set value, with volume resistivity of the different thermal expansion metal laminate being 100xcx9c150 xcexcxcexa9xc2x7cm.
Furthermore, a fuse according to the present invention is preferably has such a shape that the different thermal expansion coefficient metal laminate is wide at opposite end portions thereof and narrow at a middle melting portion.
A fuse according to the present invention is suitable for use in a battery pack. In this battery pack, a fuse melted and cut off by overcurrent is connected in series to a battery. The fuse comprises a different thermal expansion coefficient metal laminate in which a plurality of different thermal expansion coefficient metal plates are laminated, and when the fuse is melted and cut off by heat, a deforming force is applied to a melting portion, which force being caused by difference between thermal expansion coefficients of the metal plates.
A battery pack having this structure can rapidly melt and cut off a fuse and thereby can interrupt current when the battery pack is used in abnormal state. It is because a fuse connected in series to the battery comprises a different thermal expansion coefficient metal laminate in which a plurality of different thermal expansion coefficient metal plates are laminated.
In a battery pack according to the invention, a plurality of batteries can be connected in series by means of fuses. In such a battery pack, fuses each comprising a different thermal expansion coefficient metal laminate are connected to terminal electrodes of batteries arranged in parallel to each other. Fuses each comprising a different thermal expansion coefficient metal laminate are preferably connected to batteries in such a manner that, when melted and cut off by heat, the melting portion is separated from a terminal electrode of the battery, that is, it is deformed in the direction opposite to the battery.
A battery pack having this structure has an advantage that, since a melting portion of a fuse melted and cut off by overcurrent is deformed in the direction separated from a battery, the melted fuse can be prevented from attaching to the battery, thereby affording to surely interrupt current and safely use the battery pack.